Strategy is not an art; it is a science. Game Theory is the study of mathematical models of strategic interaction among rational decision-makers. It assumes that your opponent is just as smart as you are and is trying to maximize their own pay-off.
In a zero-sum game, one person's gain is exactly equal to another's loss. Poker is a zero-sum game. War, in Von Neumann's early view, often approximated this.
A scenario where two rational individuals might not cooperate, even if it appears that it is in their best interests to do so. This became the defining model for the Nuclear Arms Race.